1. Field of the Invention
The present invention relates to a radiation detection apparatus for detecting radiation.
2. Description of the Related Art
In recent years, there has been practically used a radiation detection apparatus including a fluorescent film for converting radiation especially X-rays into light, and a photoelectric conversion element for converting the light into an electrical signal. Such a radiation detection apparatus can contribute to reduction of size and weight of a radiation detection apparatus itself. The radiation detection apparatus converts image information obtained from radiation passing through an inspection object, into electrical information. The radiation detection apparatus can enjoy convenience provided by digital information processing, such as digital image processing and digital image saving.
The radiation detection apparatus has been widely used for diagnosis and treatment in a medical field including dentists, nondestructive inspection in an industrial field, and structure analysis in scientific studies, for example. Digital information processing enables extraction of high-precision images and high-speed detection of images in each field. Unexpected amount of exposure to radiation can be reduced, and speedy inspection and diagnosis can be realized.
Scintillation material technology is often diverted to a fluorescent film of a radiation detection apparatus. Scintillation material is made of material consisting mainly of Cs and I used for a conventional X-ray image tube. The scintillation material consisting mainly of cesium iodide (hereinafter, CsI) and forming a columnar crystal can increase sensitivity and resolution by an optical guide effect, compared with other scintillation materials forming a particulate crystal.
Further, a conventional X-ray image tube requires electronic lenses in a vacuum tube, and becomes large and heavy. By forming a photodetector having photoelectric conversion elements by thin film elements using amorphous silicon, a two-dimensional thin radiation detection apparatus can be made.
However, a radiation detection panel incorporated in the radiation detection apparatus consists of a photodetector having thin film elements formed on a glass substrate, and a scintillation member formed by a brittle low-strength film such as CsI formed on the photodetector. Thus, a radiation detection panel has a problem with regard to durability when subject to external mechanical stress.
To solve the above problem, Jpn. Pat. Appln. KOKAI Publication No. H11-284909 (FIGS. 1 to 5) discloses the technique to ensure space between a radiation detection panel and a housing by fixing a support base to secure the radiation detection panel and the housing. Also disclosed is the technique to place an elastic member in the housing. With this technique, external pressure can be absorbed by deforming the housing, and pressure applied to the radiation detection panel can be decreased. The above patent document also discloses the technique to arrange a shock absorption member like an air bag in the space between the housing and radiation detection panel, thereby absorbing external pressure.
Further, Jpn. Pat. Appln. KOKAI Publication No. 2002-14168 (FIG. 1) discloses the technique to use an elastic member between a housing and a radiation detection panel, and to use another elastic member between the housing and a support board to secure the radiation detection panel. By the pressing forces of the elastic members, the radiation detection panel secured to the support board is held in the housing.
However, the following problem arises in the prior art described above. The prior art aims at providing a shock absorption effect against external static pressure, and is not effective against dynamic pressure such as vibration and shock.
Namely, in Jpn. Pat. Appln. KOKAI Publication No. H11-284909, the support base to secure the radiation detection panel is fixed to the housing, and impulsive forces such as vibrations and dropping/bumping forces applied to the housing are directly transmitted to the radiation detection panel through the support base. As a result, when a dynamic force is applied to the radiation detection panel, mechanical damage is easily produced in the radiation detection panel.
In Jpn. Pat. Appln. KOKAI Publication No. 2002-14168, the elastic members are used between the housing and the support board and between the housing and the radiation detection panel. Therefore, impulsive forces such as vibrations and dropping/bumping forces applied to the housing are not directly transmitted to the radiation detection panel. However, external shock such as vibrations and dropping/bumping forces is applied as an inertial force to the support board and radiation detection panel. If the inertial force exceeds the shock absorption capacity of the elastic members, the radiation detection panel suffers a mechanical damage.
An inertial force is proportional to the mass of a substance. In a conventional example in which the radiation detection panel is secured to the support board, an inertial force is proportional to the sum of the mass of the radiation detection panel and support board. The radiation detection panel usually uses a thin glass substrate with a thickness of approximately 0.7 mm as a base member. The support board to support the glass substrate needs to be made of a rigid metallic material. In a radiation detection panel, it is further necessary to stick a lead plate to the back of the support board. The lead plate functions as an X-ray insulator for a circuit arranged on the rear side of the support board. Thus, the mass of the support board is inevitably increased to much larger than the glass substrate, and the sum of the mass of the radiation panel and support board is increased, and the inertial force is increased. This causes a problem that the inertial force exceeds the capacity of the elastic member as a shock absorption member.